Image forming apparatus, communication device, and cartridge

ABSTRACT

This invention provides an image forming apparatus which communicates with a plurality of cartridges without increasing its circuit dimension. To accomplish this, the apparatus includes a control circuit having an output terminal for outputting a clock signal and data signal used to generate a transmission signal to the cartridge, and an input terminal for receiving a transmission signal from the cartridge. The apparatus includes N connectors each having the first electrode which is connected to the first electrode surface of each cartridge, and the second electrode which is connected to the second electrode surface. The apparatus includes a 1-to-N first signal line for connecting the input terminal to the N first electrodes, and a 1-to-N second signal line for connecting the output terminal to the N second electrodes. The apparatus includes N switching units which are interposed between 1-to-N branch points and the second electrodes on the second signal line.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage Application under 35 U.S.C. §371 ofInternational Application No. PCT/JP2007/072044, filed on Nov. 7, 2007,which claims the benefit of Japanese Patent Application No. 2006-322522,filed on Nov. 29, 2006, the contents of each of which are herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates to an image forming apparatus forcommunicating data with a unit which is detachable from an electronicapparatus such as an image forming apparatus and has a storage medium.

BACKGROUND ART

Recently, information management for quality, distribution, and the likeis done by storing individual information in an enormous number ofproducts and rewriting the information by communication between theseproducts and terminals or the like.

Considering the number of products, their use environment, and the like,it is desirable to simplify the internal circuit of atransmission/reception device attached to each product and that of atransmission/reception device in the terminal in terms of downsizing,cost reduction, and durability.

Japanese Patent Laid-Open No. 2003-248798 discloses a contact typetransmission/reception apparatus which performs two-way datacommunication using two signal lines between a printer and the memorychip of a cartridge. The contact type transmission/reception apparatusdescribed in this reference minimizes the number of signal lines todecrease the number of contact connectors of the printer and that ofcontact electrode surfaces of the cartridge. This is advantageous tocost and downsizing. In general, contact type communication is effectivebetween a printer and a cartridge because the cartridge need not beinserted/removed frequently and wear hardly occurs. A contact typeapparatus for communication between a printer and a cartridge caneffectively reduce radiation noise at lower cost than by a non-contacttype apparatus which communicates using radio waves.

A printer which prints color images incorporates a plurality ofcartridges which store toners or inks in a plurality of colors. Theprinter needs to communicate with a plurality of memory chips attachedto these cartridges. However, Japanese Patent Laid-Open No. 2003-248798does not describe either a method or arrangement for communication withmemory chips. For example, a transmission/reception apparatus requiringdriving circuits equal in number to memory chips is expected to increaseits circuit dimension and greatly raise the cost.

DISCLOSURE OF INVENTION

The present invention enables realization of an image forming apparatuswhich communicates with a plurality of cartridges without increasing itscircuit dimension.

According to one aspect of the present invention, an image formingapparatus which allows detachably mounting a plurality of cartridgeshaving memories for storing information, and communicates with therespective memories of the plurality of cartridges, the apparatuscomprising:

a data transmission unit adapted to transmit a data signal to thememories of the plurality of cartridges;

a plurality of signal lines adapted to output the data signal from thedata transmission unit to the memories of the plurality of cartridges;

a control unit adapted to output the data signal to the datatransmission unit; and

switching units adapted to transmit the data signal from the datatransmission unit to one of the memories of the plurality of cartridgesby connecting the data transmission unit to one of the plurality ofsignal lines in accordance with a signal output from the control unit.

According to another aspect of the present invention, a communicationdevice which communicates data in contact with a plurality of cartridgeshaving first contacts and second contacts, the device comprising:

a data transmission unit adapted to transmit a data signal to memoriesof the plurality of cartridges;

a plurality of signal lines adapted to output the data signal from thedata transmission unit to the memories of the plurality of cartridges;

a control unit adapted to output the data signal to the datatransmission unit; and

switching units adapted to transmit the data signal from the datatransmission unit to one of the memories of the plurality of cartridgesby connecting the data transmission unit to one of the plurality ofsignal lines in accordance with a signal output from the control unit.

According to still another aspect of the present invention, a cartridgedetachably mounted in an image forming apparatus, comprising:

a first contact and second contact adapted to connect via twocommunication lines to a communication device included in the imageforming apparatus; and

a memory chip adapted to be connected to the first contact and thesecond contact,

the memory chip including a constant current circuit whose operationstate changes based on a data signal transmitted from the cartridge tothe communication device.

Further features of the present invention will be apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an arrangement of an image formingapparatus as a comparative example;

FIG. 2 is a diagram showing an example of an image forming apparatusaccording to an embodiment;

FIG. 3 is a chart showing an example of signals output from acommunication device according to the embodiment;

FIG. 4 is a diagram showing an arrangement of a memory chip incorporatedin a cartridge according to the embodiment; and

FIG. 5 is a diagram showing an arrangement of a memory chip as acomparative example.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention will now be described indetail with reference to the drawings. It should be noted that therelative arrangement of the components, the numerical expressions andnumerical values set forth in these embodiments do not limit the scopeof the present invention unless it is specifically stated otherwise.

<Image Forming Apparatus>

FIG. 1 is a block diagram showing an arrangement of an image formingapparatus as a comparative example. The arrangement of a communicationdevice 101 incorporated in an image forming apparatus 100 as thecomparative example, and one cartridge 102 detachable from the imageforming apparatus 100 will be explained. The communication device 101and cartridge 102 are in physical contact with each other, andcommunicate data via two signal lines.

The communication device 101 mainly includes a control circuit 103, areception/transmission circuit 104 including a reception circuit and adriving circuit serving as a transmission circuit, and a connector. Thecartridge 102 includes a memory chip having a memory and an interfacefor communicating data. The control circuit 103 controls datacommunication with the cartridge 102. The reception/transmission circuit104 communicates data with the memory chip based on a signal output fromthe control circuit 103. The reception/transmission circuit 104 performsdata communication using two signal lines, and thus executes all ofpower supply to the memory chip, clock supply for communicationsynchronization, and data transmission/reception.

The memory chip has an electrode surface which contacts the connectorwhen the cartridge 102 is inserted into the image forming apparatus 100.The connector and electrode surface ensure a communication line betweenthe communication device 101 and the cartridge 102. As the number ofcommunication lines decreases, the number of connectors 105 and that ofelectrode surfaces of the memory chip decrease. Hence, it isadvantageous to cost and downsizing of the system to minimize the numberof communication lines to, for example, two. Considering the demand fordownsizing, the battery life when a battery is attached, and the like,the memory chip does not have any power supply and receives power fromthe external reception/transmission circuit 104.

However, a plurality of (N) cartridges is inserted into a color imageforming apparatus or the like. If a color image forming apparatus adoptsthe arrangement in FIG. 1 without any change, it requires Nreception/transmission circuits 104. Note that N is a natural numbergreater than or equal to 2. If the number of internalreception/transmission circuits 104 increases, this leads to a largecircuit dimension and high cost. An image forming apparatus according tothe embodiment from which N cartridges are detachable will be described.The image forming apparatus according to the embodiment implements datacommunication with the cartridges using two signal lines withoutincreasing the number of internal driving circuits.

FIG. 2 is a diagram showing an example of the image forming apparatusaccording to the embodiment. The arrangement of a communication device201 incorporated in an image forming apparatus 200 according to theembodiment, and N cartridges 202, that is, 202 a, 202 b, 202 c, and 202d detachable from the image forming apparatus 200 will be explained. Inthe following description, the number (N) of detachable cartridges 202is four.

The communication device 201 comprises four connectors, a controlcircuit 203 functioning as a control unit which controls communicationwith a cartridge, a driving circuit 206 functioning as a datatransmission unit which transmits data, and a reception circuit 208functioning as a data reception unit which receives data. The cartridges202 a, 202 b, 202 c, and 202 d comprise memory chips 214, that is, 214a, 214 b, 214 c, and 214 d, respectively. Each of the memory chips 214a, 214 b, 214 c, and 214 d has two electrode surfaces (first and secondelectrode surfaces: not shown).

The connectors have first electrodes 210, that is, 210 a, 210 b, 210 c,and 210 d which are connected to the first electrode surfaces serving asthe first contacts, and second electrodes 211, that is, 211 a, 211 b,211 c, and 211 d which are connected to the second electrode surfacesserving as the second contacts. The connectors are connected to thememory chips 214 a, 214 b, 214 c, and 214 d. For example, a connectorwhich is connected to the memory chip 214 a has the first electrode 210a and second electrode 211 a, and a connector which is connected to thememory chip 214 b has the first electrode 210 b and second electrode 211b. When the cartridge 202 is mounted in the image forming apparatus 200,the electrode surface of the cartridge 202 contacts the electrode of thecommunication device 201 to form (connect) a communication line. Whenthe cartridge 202 is demounted from the image forming apparatus 200, thecommunication line is physically disconnected. The image formingapparatus allows mounting M (M is a natural number) cartridges, and thushas M connectors. However, only N cartridges equal to or smaller than Mcartridges may also be connected to the image forming apparatus. In thiscase, M-N connectors are not connected. Normally, M=N.

The control circuit 203 has an output terminal 213 for outputting aclock signal and data signal used to generate a transmission signal tothe cartridge 202, and an input terminal 212 for receiving atransmission signal from the cartridge 202. The communication device 201has a 1-to-N first signal line 204 for connecting the input terminal 212of the control circuit 203 to N first electrodes 210. The communicationdevice 201 also has a 1-to-N second signal line 205 for connecting theoutput terminal 213 to the second electrodes 211. More specifically, thefirst signal line 204 branches from branch points 215 b, 215 c, and 215d, and is connected to each first electrode 210. The second signal line205 branches from branch points 216, that is, 216 b, 216 c, and 216 d,and is connected to each second electrode 211.

The communication device 201 further comprises four switching units 207,that is, 207 a, 207 b, 207 c, and 207 d which are interposed between thebranch points 216 and the second electrodes 211 on the second signalline. The switching units 207 a, 207 b, 207 c, and 207 dconnect/disconnect the second electrodes 211 to/from the output terminal213 based on a switching signal S3 output from the control circuit 203.The switching signal is also used to alternatively select a cartridgeserving as a communication partner, and may also be called a selectionsignal. More specifically, the control circuit 203 controls theswitching unit 207 a to the connection state and the switching units 207b, 207 c, and 207 d to the disconnection state based on the switchingsignal S3. In this case, the communication device 201 communicates datawith the cartridge 202 a. The communication device 201 according to theembodiment can selectively communicate data with one of the cartridges202 by changing one of the switching units 207 a to 207 d to theconnection state and the others to the disconnection state.

The switching units 207, that is, 207 a to 207 d are desirably formedfrom field-effect transistors (to be referred to as FETs hereinafter).This is because the FET is much smaller in size than a mechanical switchtypified by a relay and lower in cost than a selector circuit formedfrom a semiconductor element, and the circuit arrangement and circuitpattern layout can be designed at high degree of freedom.

A principle which allows selective data communication by arranging theswitching units 207 on only the second signal line 205 will beexplained. Assume that the communication device 201 communicates datawith the cartridge 202 a in FIG. 2. The control circuit 203 outputs theswitching signal S3 to enable the gate signal of the FET serving as theswitching unit 207 a. The control circuit 203 disables the gate signalsof the FETs serving as the switching units 207 b, 207 c, and 207 d. As aresult, only the memory chip 214 a is connected to the second signalline 205. The remaining memory chips 214 b, 214 c, and 214 d areconnected to only the first signal line 204, and the second signal line205 is open to them. The first and second electrode surfaces of thememory chips 214 b, 214 c, and 214 d have no difference in potential.Only the memory chip 214 a becomes active, and the memory chips 214 b,214 c, and 214 d become inactive. In this way, the image formingapparatus 200 according to the embodiment can execute selective datacommunication by ON/OFF-controlling the switching unit 207 inserted inonly one of the two signal lines connected to the memory chip 214serving as a communication partner.

The driving circuit 206 is interposed between the output terminal 213and the switching units 207 on the second signal line 205. The drivingcircuit 206 supplies power via the second signal line 205 to thecartridge 202 whose second electrode 211 is connected by the switchingunit 207. The driving circuit 206 outputs a transmission signal based ona clock signal and data signal from the control circuit 203. Thetransmission signal is obtained by superposing information acquired fromthe data signal on the clock signal output from the control circuit 203.According to the embodiment, even when the four cartridges 202 aremounted, the image forming apparatus can perform selective datacommunication with one cartridge 202 selected by the switching unit 207.This obviates the need to arrange four driving circuits 206 incorrespondence with the memories of four cartridges.

The reception circuit 208 is interposed between the input terminal 212and the first electrode 210 on the first signal line 204, and receives atransmission signal from the cartridge 202 corresponding to the secondelectrode which is connected by the switching unit 207. The receptioncircuit 208 is commonly connected to the cartridges 202 via the firstsignal line 204. This arrangement is possible because the image formingapparatus performs selective data communication with one cartridge 202selected by the switching unit 207. That is, a signal is always outputfrom only the memory chip 214 of one cartridge 202. This obviates theneed to arrange four reception circuits 208, and one reception circuit208 suffices to be connected commonly.

As described above, the communication device 201 according to theembodiment switches the second signal line 205 by the switching unit207. The control circuit 203 turns off the FETs serving as the switchingunits 207 to disconnect the second signal line 205 from the memory chips214 of the cartridges 202 other than a communication partner. Inpractice, however, even if the FET is turned off, a parasiticcapacitance always exists between the drain and source terminals of theFETs. When the driving circuit 206 generates a pulse, even an FET in theOFF state transmits the AC component, and the AC voltage is applied tothe memory chip 214 other than a communication partner. To solve thisproblem, the communication device 201 includes four charge accumulationunits. Each charge accumulation unit has one end connected to the firstsignal line 204, and the other end connected between the secondelectrode 211 and the switching unit 207 on a corresponding secondsignal line 205. The embodiment uses, for example, condensers 209, thatis, 209 a, 209 b, 209 c, and 209 d as the charge accumulation units. Byconnecting the condensers 209 a, 209 b, 209 c, and 209 d, the followingapproximate expression is established:

$\begin{matrix}{{VM} \approx {{VAB} \times \frac{C\; 2}{{C\; 1} + {C\; 2}}}} & (1)\end{matrix}$

For example, VAB represents the voltage difference between a signal Aoutput to the second signal line 205 and a signal B output to the firstsignal line 204. VM represents the voltage applied between the twoterminals of the first and second electrode surfaces of the memory chip214 other than a communication partner. C1 represents the capacitance ofthe condenser 209. C2 represents the parasitic capacitance between thedrain and source of the FET.

Strictly speaking, a current detection resistor R1 and the internalimpedance of the memory chip 214 shown in FIG. 2 need to be considered.However, the approximate calculation ignores these impedances oncondition that the impedance of the condenser 209 is reduced. LettingVOFF be the voltage between terminals for reliably stopping (turning offor resetting) a memory chip, the capacitance value of the condenser 209need to be determined to satisfy VM<VOFF. Letting VOFF=0.1 V, VAB=5 V,and C2=20 pF, the capacitance value C1 is calculated to be 980 pF ormore in accordance with expression (1). When the communication frequencyis set to about 100 kHz, the impedance of the condenser 209 iscalculated to be about 1.6 kΩ. The internal impedance of the memory chip214 is at least several times this value. The impedance of the condenser209 is dominant over the synthesized impedance of parallel connectionwith the condenser 209.

By inserting the 980 pF condenser, the impedance between the twoterminals of the memory chip 214 other than a communication partnerbecomes much lower than an impedance generated by the parasiticcapacitance between the drain and source of the FET. Even if the drivingcircuit 206 applies an AC voltage, the voltage applied between the twoterminals of the memory chip 214 can be suppressed to a voltage or lowerat which the memory chip 214 stops. In practice, a value obtained bysubtracting a voltage drop by the current detection resistor R1 fromthis voltage represents a voltage applied to the memory chip 214. Thememory chip 214 can reliably stay OFF.

For the contact type communication device, various communication methodsare proposed depending on the number of signal lines. As the number ofsignal lines increases, the total cost including cabling and connectorsrises. To implement a system at the smallest size and lowest cost, atwo-line communication method using two signal lines at minimum iseffective. The communication device 201 according to the embodiment canimplement two-line data communication without increasing the numbers ofdriving circuits 206 and reception circuits 208 even when a plurality ofcartridges 202 is mounted. The communication device 201 can performselective data communication by inserting the switching units 207 inonly one of the two signal lines. One switching unit 207 is sufficientfor one memory chip 214, and this arrangement is advantageous to evencost without increasing the circuit dimension.

<Details of Communication Method>

Details of the communication method will be described. Datacommunication by downlink and uplink between the driving circuit 206 andthe memory chip 214 will be explained. “Downlink” means datatransmission from the control circuit 203 to the memory chip 214.“Uplink” means data transmission from the memory chip 214 to the controlcircuit 203.

(1) Downlink Operation

FIG. 3 is a chart showing an example of signals output from thecommunication device according to the embodiment. Signals output to thefirst signal line 204 and second signal line 205 in downlink will beexplained.

A signal A 301 shown in FIG. 3 is output to the second signal line 205in downlink. A signal B 302 is output to the first signal line 204 indownlink. An internal CLK 303 is a clock signal generated in synchronismwith the leading edge of the signal A 301 within the memory chip 214.

The signal B 302 is grounded via the current detection resistor R1 shownin FIG. 2. The current detection resistor R1 has a small resistancevalue around several ten Ω for detecting a reception signal, which willbe described later. Hence, the signal B 302 functions as a ground signalat almost 0 V. The signal A 301 is an output from the driving circuit206, and is obtained by superposing information acquired from a datasignal on a clock signal. More specifically, as shown in FIG. 3, thesignal A 301 is a modulating signal which changes between two values VHand VL at a predetermined cycle T1 (communication frequency). Thevoltage of the signal A 301 is always equal to or higher than VL.

The internal CLK 303 is an ON duty signal having a predetermined delayT2 from the leading edge of the signal A 301. The time, that is, pulsewidth during which the signal A 301 is at the voltage VH is adjustedbased on output data (“H” or “L”). As shown in FIG. 3, the signal A 301is adjusted to a pulse width T3 for data “H” and a pulse width T4 fordata “L”. At this time, it is important to satisfy T4<T2<T3. Each memorychip 214 can receive data by determining whether the signal A 301 is atthe level VH or VL when the internal CLK 303 falls.

An internal operation of the memory chip 214 in downlink will bedescribed with reference to FIG. 4. FIG. 4 is a diagram showing anarrangement of the memory chip incorporated in the cartridge accordingto the embodiment. The memory chips 214 a, 214 b, 214 c, and 214 d havethe same arrangement, so the arrangement of the memory chip 214 a willbe exemplified.

The memory chip 214 a comprises a detection circuit 401 for detecting avoltage level, a clock generation circuit 402 for generating an internalCLK, a detection circuit 403 for detecting data, a control circuit 404,a regulator circuit 405, a constant current circuit 406, and a memory407. The regulator circuit 405 outputs a predetermined voltage. Theconstant current circuit 406 will be explained in a description of datacommunication in uplink.

The detection circuit 401 detects the voltage level of the signal A 301which changes between the two values VH and VL. The clock generationcircuit 402 generates the internal CLK 303 in accordance with change ofa detection signal output from the detection circuit 401. As shown inFIG. 3, the internal CLK 303 has a pulse width obtained by adding thedelay T2 to a leading edge from VL to VH. The detection circuit 403determines whether an output from the detection circuit 401 is at VH orVL at the falling edge of the internal CLK 303. More specifically, thedetection circuit 403 detects data “H” when the signal A 301 has thepulse width T3 and data “L” when it has the pulse width T4. Thedetection circuit 403 outputs the detection result as reception data tothe control circuit 404.

(2) Uplink Operation

Data communication in uplink will be explained with reference to FIGS. 4and 5. FIG. 5 is a diagram showing an arrangement of a memory chip as acomparative example.

As shown in FIG. 5, a memory chip 500 is connected by two connectors 502and 503 to a driving circuit 501 including a reception circuit. Thememory chip 500 comprises an internal CLK generation circuit 504, datadetection circuit 505, control circuit 507, regulator circuit 508,memory 509, switch 510, and resistor 511. The internal CLK generationcircuit 504, data detection circuit 505, control circuit 507, regulatorcircuit 508, and memory 509 perform the same operations as those of theelements shown in FIG. 4.

As shown in FIG. 5, the switch 510 and resistor 511 are series-connectedand interposed between two signal lines which transmit signals A and Bin the memory chip 500. The control circuit 507 ON/OFF-controls theswitch 510 based on data to be transmitted from the memory chip 500 tothe driving circuit 501. In response to this, the consumption current ofthe memory chip 500 changes between two values. The communication device201 detects the current and can receive data.

In the embodiment, as shown in FIG. 4, the memory chip 214 includes theconstant current circuit 406 requiring a current I2. The control circuit404 in the memory chip 214 ON/OFF-controls the operation state of theconstant current circuit 406 based on transmission data, therebyoutputting a signal. In addition to the consumption current I2 of theconstant current circuit 406, the current is steadily consumed by alogic operation and memory access operation within the memory chip 214.Letting I1 be this current value, the currents of the signals A and Bchange between the two values I1 and I2. The reception circuit 208extracts these currents as voltages at the current detection resistorR1. Accordingly, the communication device 201 receives data output fromthe cartridge 202.

In the embodiment, a memory chip serving as a communication partner isselected by ON/OFF-controlling only one of the two signal lines usingFETs in order to communicate with a plurality of memory chips 214. Asshown in FIG. 2, the reception circuit 208 is inserted in the othersignal line which is not disconnected by the FETs. The reception circuit208 need not be switched depending on the memory chip 214 serving as acommunication partner, and the communication device 201 suffices toinclude only one common reception circuit 208. The communication device201 can communicate data with a plurality of cartridges at low costwithout increasing the circuit dimension.

It is important for reception based on current detection to connect thecondenser 209 to a ground potential V1, as shown in FIG. 2. Assume thatthe condenser 209 is connected not to the ground potential V1 but to aterminal on the side of the memory chip 214 out of the two terminals ofthe current detection resistor R1. In this case, an AC current havingpassed through a capacitive component path formed by the memory chip 214other than a communication partner and a corresponding switching unit207 passes through the current detection resistor R1. As a result, thevoltage detection margin of a comparator CMP1 decreases. A voltage dropat the current detection resistor R1 becomes large in switching, and thecommunication waveform distorts, adversely affecting communication.

By connecting the condenser 209 to the ground potential V1, anunnecessary current component passing through the current detectionresistor R1 can be reduced to improve the detection precision of thereception circuit 208. The embodiment has described a method of settinga signal having a lower potential out of two transmission signals to afixed voltage (ground potential V1 shown in FIG. 2), and modulating asignal having a higher potential. However, the same effects can also beattained by setting a signal having a higher potential to a fixedvoltage (V1 is not the ground potential but a reference potential), andmodulating a signal having a lower potential, details of which will notbe described. In the embodiment, a signal on the side of the drivingcircuit out of two signals is enabled/disabled by the FET. However, thesame effects can also be obtained by enabling/disabling a signal on theside of the reception circuit by the FET.

As described above, in the image forming apparatus according to theembodiment, the communication device communicates data with a pluralityof cartridges using the two, first and second signal lines. The imageforming apparatus includes switching units which connect or disconnectthe second signal line. The image forming apparatus can selectivelycommunicate data via the two signal lines, and does not require aplurality of driving circuits corresponding to a plurality ofcartridges. The image forming apparatus can, therefore, communicate datawith a plurality of cartridges without increasing the circuit dimension.The image forming apparatus can achieve selective data communication byinserting the switching units in only one signal line. Thus, the imageforming apparatus can prevent an increase in circuit dimension andreduce the cost.

The present invention is not limited to the above-described embodiment,and can be variously modified. The image forming apparatus may include Ncharge accumulation units each having one end connected to the firstsignal line, and the other end connected to a branched second signalline between the second electrode and the switching unit. With thisarrangement, the image forming apparatus can further increase theswitching precision of the switching unit. The image forming apparatuscan selectively communicate data via the two signal lines. The imageforming apparatus can communicate data with a plurality of cartridgeswithout increasing the circuit dimension.

The image forming apparatus may further include a reception circuitwhich is inserted in the first signal line and receives a signal outputfrom the cartridge. Even when the image forming apparatus communicatesdata with a plurality of cartridges, only one reception circuit insertedin the first signal line can receive a signal output from eachcartridge. The image forming apparatus can communicate data with aplurality of cartridges without increasing the circuit dimension.

The reception circuit may also include a current detection resistorconnected to the reference potential or ground potential within thereception circuit. In this case, the charge accumulation unit may alsobe connected to the reference potential or ground potential to which thecurrent detection resistor is connected. In the image forming apparatus,it is also possible to set a signal having a lower potential out of twosignals to a fixed voltage, and modulate a signal having a higherpotential. In the image forming apparatus, it is also possible to set asignal having a higher potential to a fixed voltage, and modulate asignal having a lower potential. The image forming apparatus enables aflexible design.

According to the embodiment, the switching unit may also be formed froma field-effect transistor (FET). The FET is much smaller in size than amechanical switch typified by a relay and lower in cost than a selectorcircuit formed from a semiconductor element, and the circuit arrangementand pattern layout can be designed at high degree of freedom. Even whenthe image forming apparatus communicates data with a plurality ofcartridges, the circuit dimension can be further reduced.

The present invention can provide an image forming apparatus whichcommunicates with a plurality of cartridges without increasing itscircuit dimension.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-322522, filed on Nov. 29, 2006, which is hereby incorporated byreference herein in its entirety.

1. An image forming apparatus to which a plurality of cartridges havingmemories for storing information are detachably mounted, wherein theimage forming apparatus communicates with the respective memories of theplurality of cartridges, the apparatus comprising: a data transmissionunit adapted to transmit a data signal to the memories of the pluralityof cartridges; a plurality of transmission signal lines adapted tooutput the data signal from said data transmission unit to the memoriesof the plurality of cartridges; a control unit adapted to output thedata signal to said data transmission unit; switching units adapted toconnect said data transmission unit to one of said plurality oftransmission signal lines in accordance with a signal output from saidcontrol unit so as to transmit the data signal from said datatransmission unit to one of the memories of the plurality of cartridges;a data reception unit adapted to receive a data signal transmitted fromone of the memories of the plurality of cartridges; and a plurality ofreception signal lines adapted to transmit a data signal from thememories of the plurality of cartridges to said data reception unit,wherein transmitting the data signal to said data reception unit isperformed using one of the plurality of reception signal lines which isconnected to the memory of the cartridge which can communicate with saiddata transmission unit in accordance with a connection, performed bysaid switching units, of said data transmission unit to one of saidplurality of transmission signal lines.
 2. The apparatus according toclaim 1, wherein said control unit selectively executes output of thedata signal from said data transmission unit and reception of the datasignal by said data reception unit.
 3. The apparatus according to claim2, wherein the cartridges have first contacts and second contacts, saidcontrol unit has an output terminal which outputs a clock signal and thedata signal to said data transmission unit in order to generate atransmission signal to the cartridges, and an input terminal whichreceives a signal transmitted from said data reception unit, the imageforming apparatus further comprises a plurality of connectors havingfirst electrodes which are connected to the first contacts of theplurality of cartridges and second electrodes which are connected to thesecond contacts, the reception signal lines include a reception signalline for connecting the input terminal to the first electrodes, and thetransmission signal lines include a transmission signal line forconnecting the output terminal to the second electrodes, said switchingunits are inserted between the output terminal and the second electrodesof the transmission signal, and switch connection states between thesecond electrodes and said data transmission unit based on a switchingsignal output from said control unit, and said data transmission unitincludes a driving circuit which is interposed between the outputterminal and said switching units on the transmission signal line forconnecting the output terminal to the second electrodes, supplies powervia the transmission signal line to a memory of a cartridgecorresponding to a second electrode connected by said switching units,and outputs a transmission signal based on the clock signal and the datasignal.
 4. The apparatus according to claim 3, further comprising aplurality of charge accumulation units each having one end connected tothe reception signal line for connecting the input terminal to the firstelectrodes, and the other end connected between the second electrode andsaid switching units on a corresponding transmission signal line.
 5. Theapparatus according to claim 3, wherein said data reception unitincludes a reception circuit which is interposed between the inputterminal and the first electrode on the reception signal line forconnecting the input terminal to the first electrodes, and receives asignal from a cartridge corresponding to a second electrode connected bysaid switching units.
 6. The apparatus according to claim 5, whereinsaid reception circuit includes a current detection resistor which isinterposed between the first electrode and a reference potential orground potential in said reception circuit, and detects a current of atransmission signal output from the cartridge to the reception signalline for connecting the input terminal to the first electrodes, and oneend of each charge accumulation unit is connected to the referencepotential or ground potential to which the current detection resistor isconnected.
 7. The apparatus according to claim 3, wherein said switchingunit includes a field-effect transistor which receives the switchingsignal at a gate.
 8. A communication device which communicates data andis in contact with a plurality of cartridges, the device comprising: adata transmission unit adapted to transmit a data signal to memories ofthe plurality of cartridges; a plurality of transmission signal linesadapted to output the data signal from said data transmission unit tothe memories of the plurality of cartridges; a control unit adapted tooutput the data signal to said data transmission unit; and switchingunits adapted to connect said data transmission unit to one of saidplurality of transmission signal lines in accordance with a signaloutput from said control unit so as to transmit the data signal fromsaid data transmission unit to one of the memories of the plurality ofcartridges; a data reception unit adapted to receive a data signaltransmitted from one of the memories of the plurality of cartridges; anda plurality of reception signal lines adapted to transmit a data signalfrom the memories of the plurality of cartridges to said data receptionunit, wherein transmitting the data signal to said data reception unitis performed using one of the plurality of reception signal lines whichis connected to the memory of the cartridge which can communicate withsaid data transmission unit in accordance with a connection, performedby said switching units, of said data transmission unit to one of saidplurality of transmission signal lines.
 9. The device according to claim8, wherein said control unit selectively executes output of the datasignal from said data transmission unit and reception of the data signalby said data reception unit.